In general, typical control signals outputted from temperature controllers to control a load are a relay output for controlling a relay, an SSR output for driving an SSR (Solid State Relay), and a current output of 4 to 20 mA outputted as a current signal having a magnitude corresponding to a control target value within a present range.
In order to accurately control temperature, an SCR phase controller or an SCR zero-cross cycle controller 20 outside a temperature controller 10 is connected to a terminal outputting current at 4 to 20 mA, as shown in FIG. 1, in which it is possible to increase/decrease heating value of a load 40, for example, a heater, by increasing/decreasing power supplied to the load from an AC power supply to control temperature of the load 40 to a target temperature, in accordance with temperature of the load 40 which is sensed by a temperature sensor 30.